Noonan and LEOPARD syndromes (NS and LS) are autosomal dominant traits with features that include congenital heart disease (CHD), short stature, dysmorphism, and mental retardation; LS also includes lentigines. We have shown that PTPN11 missense mutations cause nearly 50% of NS and engender gain-of- function on its protein, the protein tyrosine phosphatase SHP-2. Loss-of-function PTPN11 mutations cause LS. Recently, we found that KRAS mutations cause 1% of NS. SHP-2 and KRAS play roles in RAS-mitogen activated protein kinase (MAPK) signaling. SPECIFIC AIM 1 will test the hypothesis that the unknown NS genes encode proteins in RAS-MAPK signaling. Candidate genes will be resequenced in a high throughput fashion with a large cohort of NS subjects without PTPN11 or KRAS mutation. Biochemical and cell culture approaches will be used to test the effects of mutations on novel NS genes. In SPECIFIC AIM 2, we hypothesize that SHP-2 mutants cause LEOPARD syndrome through gain-of-function effects on development despite their reduced phosphatase activity and that NS-associated KRAS mutations alter signaling more profoundly than do NS PTPN11 defects. To test these ideas, we will generate transgenic fruit flies inducibly expressing homologous NS and LS mutant proteins. Their phenotypes and genetic interactions will be characterized. Further, we hypothesize that genes interacting genetically with the Egfr-related wing phenotype from the existing NS fruit fly model will identify novel aspects of signal transduction as well as new NS disease genes. A sensitized screen will be performed to identify genes that suppress or enhance that wing phenotype.